The invention relates to the field of magnetic transducers (heads) having inductive write heads and more particularly to the structure of a pole piece and a method for forming a pole piece tip for the write head.
A typical prior art head and disk system is illustrated in FIG. 1. In operation the magnetic transducer 10 is supported by a suspension 13 as it flies above the disk 16. The magnetic transducer, usually called a xe2x80x9chead,xe2x80x9d is composed of elements that perform the task of writing magnetic transitions (the write head 23) and reading the magnetic transitions (the read head 12). The electrical signals to and from the read and write heads 12, 23 travel along conductive paths 14 which are attached to or embedded in the suspension 13. Typically there are two electrical contact pads each for the read and write heads 12, 23. Wires or leads are connected to these pads (not shown) and routed in the suspension 13 to the arm electronics (not shown). The disk 16 is attached to spindle 22 that is driven by the spindle motor 24 to rotate the disk. The disk 16 comprises a substrate 26 on which a plurality of thin films 21 are deposited. The thin films include ferromagnetic material that is used to record the magnetic transitions in which information is encoded.
The write head 23 portion of the transducer 10 includes two pole pieces (P1 and P2) and a coil (not shown). To decrease the side writing and, therefore, to reduce the track width the pole pieces are shaped into narrow tips at the gap (not shown). To be effective the P1 tip should be the same size as the P2 pole tip and should extend up from the larger body of P1 pole piece about 1 to 1.5 times the gap thickness. In one prior art method P1 is deposited first and initially has a broad, flat tip that is subsequently ion milled using the P2 tip as a mask to form the P1 tip. Since the top surface of P2 is also exposed to milling during this process, the P2 layer must initially be thicker than the final desired thickness. For the same reason it is necessary to protect all regions of the wafer that would be harmed by the milling.
Variations of this process are described in U.S. Pat. No. 6,119,331 to Chen, et al.; U.S. Pat. No. 5,452,164 to Cole, et al.; and U.S. Pat. No. 5,438,747 to Krounbi, et al. Chen ""331 describes the use of a notching layer that is deposited by plating on top of the initial P1 layer which is also plated. The ion milling can then proceed until only the notching layer outside of the desired tip area is removed or it can proceed to also mill away some of the initial P1 layer. The notching layer, therefore, contributes the P1 tip in this design and must be ferromagnetic.
One problem with all of the prior art ion milling methods is that it is difficult to determine the precise point at which milling should stop. In current practice the end point must be determined by experimentation with the particular equipment and materials being used.
Applicant discloses a magnetic transducer with a bilayer pole piece in which a first layer of material forms the body of the pole piece and a second layer forms the pole tip after milling. The described embodiment of the invention is in a head with a bilayer P1 comprising a body and a tip. The process of making the head proceeds conventionally through plating of the P1 layer which in applicant""s head is the layer which forms the body of P1. The process of the invention deposits a P1 protection layer and then uses a photo lift-off technique to form a void in the P1 protection layer where the gap and the P1 and P2 tips will be formed, i.e., the zero throat region. An additional ferromagnetic layer that will be called the xe2x80x9cP1 tip layerxe2x80x9d is vacuum deposited on the P1 protection layer and the void area to a thickness equal to the final desired pole tip height. The gap layer is deposited and the P2 tip is formed as in the prior art. Ion milling is then performed as in the prior art with the exceptions: 1) that the P1 protection layer protects areas of the wafer which should not be milled; and 2) instead of milling a notch in the planar surface of P1, only the excess of the P1 tip layer is required to be milled. A disk drive using the magnetic transducer of the invention is also described. The Applicant also discloses a method to improve the determination of the optimum stopping point for the ion milling using the optically observable process of the gap layer and P1 tip layer being milled off of the P1 protection layer forming a gradually disappearing halo.